There has been a great deal of interest in developing better and more efficient methods for storing energy for applications such as radio communication, satellites, portable computers and electrical vehicles to name but a few. There have also been concerted efforts to develop highpower, cost effective batteries having improved performance characteristics, particularly as compared to storage system in the art.
Currently available battery systems are either primary (i.e., not rechargeable) or secondary (rechargeable). Each system has advantages for different applications. For example, electrodes for rechargeable batteries may be regenerated many times by the application of an electrical charge thereto. As a result, rechargeable batteries are preferred for many consumer electronic applications. Conversely, primary cells are not rechargeable, however, primary cells are made to hold a greater charge and hence are preferred in applications in which longer life is required.
Heretofore, the electrode has usually been composed of a metal grate or foil for current collection attached to, or having attached thereto, a layer or layers of porous electrochemically active material. Sintered metal matrices have also been used to eliminate or reduce the need for the metal foil. The advantage of using a sintered material is that it provides higher surface area for the hetrogenous electrochemical reactions to take place. However, most porous matrices exhibit relatively poor electrical conductivity. Accordingly, a current collector/grid is preferred if highpower applications are required.
Heretofore, the active materials used in such cells were produced by one or more of the following methods:
(1) via chemical reaction such as lead/lead oxide in a lead acid battery;
(2) electrolytic impregnation such as nickel hydroxide/nickel oxyhydroxide in a nickel battery;
(3) sintered electrodes as is employed in the metal hydroxide electrode of a nickel-metal hydride battery;
(4) powder or fiber bonded by Teflon or other binders as is commonly employed in nickel electrodes; and
(5) pressed powders such as high-surface area carbon in double-layered capacitors.
Each of the methods described above relies on the use of powders as the starting materials. The powders typically have powder particle size in the range of a few microns to a few hundred microns. Since most oxides/hydroxides are not conductive, once the surface of the powder is converted, the core of the particle is blocked from further reaction. Thus, utilization of the active material is generally low in most conventional battery materials.
Therefore, there exists a need for a new technology which does not rely on the powder metallurgy processes characterized by the prior art and hence enhances the surface to volume ratio so as to improve the electrochemical performance of the electrode material. Moreover, such a material should be readily fabricated by readily available, commercially proven fabrication techniques.